1. Field of the Invention
The invention relates to an apparatus for storing, feeding and measuring yarn, particularly the weft yarn in a jet loom.
2. Description of Related Art
It is known to provide an apparatus for storing, feeding and measuring yarn, particularly the weft yarn in a jet loom, comprising a stationary storage drum adapted to have a temporary yarn supply wound thereonto by means of a winder appliance, and to have the yarn withdrawn therefrom over a withdrawal end. An annular housing surrounds the storage drum with an annular gap defined therebetween. The annular housing carries at least one yarn stopper device comprising a stop member mounted for radial displacement between a passive position away from the annular gap and a stop position extending through the annular gap. At least one current-energizable solenoid is provided as an actuator for said stop member. Abutment stops are provided for limiting the displacements of the stop member.
In apparatus of this type known from European Patent 107,110 and European Patent Application 148,356(which correspond to U.S. Pat. No. 4,541,462), the stop member is a ball of a ferromagnetic material mounted for back and forth displacement between a permanent magnet disposed at a recessed position with respect to the surface of the storage drum and acting as one of said abutment stops, and the stationary core of the solenoid acting as the other abutment stop, the axis of said solenoid being aligned in the radial direction. As long as the solenoid is deenergized, the ball is retained on the permanent magnet, and the annular gap is open for the passage therethrough of the yarn. When the solenoid is energized, it generates a magnetic force overcoming the holding force of the permanent magnet, so that the ball is attracted by the core of the solenoid and retained thereon as long as the solenoid is energized. In this position the ball blocks the annular gap, preventing the yarn from passing therethrough for a predetermined period of time. As soon as the solenoid is deenergized, the ball returns to the permanent magnet.
In a similar apparatus known from EP-A-0 112 555 and EP-A-0 111 308, the solenoid is aligned in a radial direction with respect to the drum surface and provided with a magnet armature having a pin-shaped extension adapted on energization of the solenoid to be pushed into a recess formed in the drum surface to thereby block the annular gap, whereas in the deenergized state of the solenoid it is retracted by a retraction spring and retained in its passive position. The same principle is known from DE-GM 84 29 220.
In these known embodiments of the apparatus, the solenoids of the stopper devices are of a heavy-duty type, i.e. relatively strong and bulky, or provided with a great number of windings, resulting in an undesirable increase of the dimensions of the annular housing. The energization of the solenoid for the full duration of the stop position results in a considerable load acting thereon, and thus in undesirable heating of the solenoid. When, as is usually the case, a great number of stopper devices with associated solenoids is provided along the periphery of the storage drum, the amounts of heat generated by the selective and successive energization of the solenoids accumulate, so that additional cooling provisions may be required in the case of extended and continuous operation. A further serious disadvantage of the known apparatus is the shifting inertia, i.e. the slow response of the stop members due to their considerable mass to be displaced. There is a growing tendency to reduce the dimensions of apparatus of this type in consideration of the restricted installation space in a loom, which may have to accommodate up to eight or even more such devices on one side. The reduction of the dimensions of these devices results in a considerably increasing revolution speed of the yarn exit point about the withdrawal end of the storage drum, This speed being still further increased by the fact that modern looms are operated at progressively higher weft yarn shooting speeds. A rapid and smooth response and short shifting times of the stop members are therefore of growing importance in devices of this type, in combination with the requirement to keep their structural dimensions as small as possible and to avoid any excessive generation of tangible heat. In the known embodiments of the apparatus, finally, the required energization of the selected solenoid for the full duration of the stop position represents a further danger, because the usually employed transistor control circuit of the solenoid may collapse under the effect of the high load, resulting in a possibly dangerous overload of the solenoid and the consequent generation of excessive heat.
It is an object of the present invention to provide an apparatus of the type defined in the introduction, which is to be characterized by compact exterior dimensions, rapid and smooth response and short shifting times of the stop members, and reduced loads acting on the solenoids.